Polychlorinated biophenyls (PCBs) are major environmental contaminants of public concern, and have been listed as priority toxic pollutants. Development of a cost-effective biological treatment method is of significance for the clean-up of PCB-contaminated soils and sediments. The objectives of this project are to develop anaerobic microbial consortia which are capable of dechlorinating and degrading PCBs, and demonstrate the feasibility of utilization of the consortia to clean-up PCB-contaminated river and lake sediments. Our results to date have indicated that PCBs were completely dechlorinated to non-chlorinated compounds. GC-MS and thermal desorption-GC-MS were used as key tools to identify the intermediate products during anaerobic dechlorination of PCBs. According to mass spectral data, PCBs were completely dechlorinated to biphenyl by the microbial consortia. In the future, more mass spectral analysis will be required for the identification of other dechlorinated intermediates or products and understanding the performance of biotreatment of PCBs.